This invention relates to electronic ignition systems for internal combustion engines.
Published European Application No. 0 071 910 A2 discloses an electronic ignition system having individual spark plug ignition devices as well as an additional ignition device common to all spark plugs. In that system, transistor ignition devices with current regulation are used as the individual spark plug ignition devices and the common ignition device contains a regulated direct-current converter connected, by way of diodes, to the secondary windings of the ignition coils of those ignition devices. Both types of ignition devices may be controlled or regulated as a function of parameters of the internal combustion engine, such as rpm, load and knocking.
A disadvantage of this prior art ignition system is that essentially only a single ignition pulse is supplied by the direct-current converter for each ignition process. As a result, difficulties may occur in ignition with a lean mixture, especially in operating modes of the internal combustion engine which are of interest in view of modern reduced emission objectives.
In this respect, more favorable behavior is provided by a programmable transistor ignition system, hereinafter called a "PTI", such as is disclosed in German Offenlegungsschrift No. 23 40 865. That PTI contains an electronic switch connecting a direct-current voltage source into an output transformer and having a switching frequency which is a multiple of the firing frequency of each spark plug. Like the conventional ignition device, the PTI is controllable according to operating and environmental parameters. A disadvantage of this known PTI is the requirement for a mechanical distributor, which is known to be relatively susceptible to trouble. In addition, the PTI does not supply very precisely timed ignition sparks.